The present invention is directed to an MOR zeolite membrane having mordenite zeolite crystals dominantly oriented in a specific crystalline direction on a porous substrate and a method for producing the membrane. Zeolite has a frame or matrix structure of crystalline aluminosilicate, which includes a mesh-like structure composed of fine pores having a minute and uniform diameter. Thus, zeolite is used as a molecular sieve or a catalyst.
For example, JP-A-7-330326 discloses a zeolite membrane which is formed on a single crystal substrate of an oxide, a semiconductor or a metal, and having crystals oriented in a specific crystalline direction. Zeolite membranes of the A type, Y type and Method for Producing the Same the like are disclosed in the examples in JP ""326.
In addition, WO92/13631 discloses zeolite membranes including an oriented single crystal layer of ZSM-5 (MFI), an A type, a Y type, an X type and the like. WO97/25272 discloses an MFI zeolite membrane having crystals oriented along the b-axis and a method for producing the membrane. Further, WO96/01683 discloses an MFI zeolite membrane having crystals oriented along the a-axis and the c-axis and the method for producing the membrane.
However, a mordenite (MOR) zeolite membrane having crystals oriented in a specific crystalline direction has not yet been known. An MOR zeolite membrane is superior in acid resistance in comparison with other zeolite membranes, such as, for example, those of an A type, a Y type and the like. Thus, such an MOR zeolite membrane would be greatly desired and extremely useful in a wide variety of applications.
The present invention has been made in view of the problems associated with the prior art, and a goal of which is to provide an MOR zeolite membrane having crystals dominantly oriented in a specific crystallization direction and a method for producing the membrane. That is, according to the present invention, there is provided a mordenite (MOR) zeolite membrane formed on a porous substrate and having crystals dominantly oriented in a specific crystalline direction.
According to the present invention, there is further provided a method for producing a mordenite (MOR) zeolite membrane including the steps of:
immersing a porous substrate in a gel of raw material which contains zeolite constitution elements and contains 40-400 of SiO2/Al2O3 in molar ratio, 10-120 of H2O/Na2O in a molar ratio, and 10-40 of H2O/SiO2 in molar ratio; and
subjecting the gel in the presence of the porous substrate to a hydrothermal synthesis at 150xc2x0 C. or more to crystallize the zeolite to form a membrane thereof.
In the above, it is preferable that the porous substrate is disposed in a reaction vessel so that a surface on which a membrane is formed becomes perpendicular, and that the gel of the raw material contains SiO2/Al2O3 of 100-400 in molar ratio, H2O/Na2O of 10-100 in molar ratio, and H2O/SiO2 of 10-30 in molar ratio.